The present invention relates to an optical fiber suitable for wavelength division multiplexing (WDM) transmission and an optical transmission line using this optical fiber in at least one portion.
As high speed and large capacity of optical transmission is advanced, a wavelength division multiplexing (WDM) transmission technique is noticed as a key technique. However, a non-linear phenomenon caused by high input signal power or signal interactions is discussed as a new problem.
Among the non-linear phenomena, four-wave mixing (FWM) has a serious influence on the WDM transmission. Therefore, a restraining method of the four-wave mixing is vigorously studied. Since the FWM is caused with small dispersion, it is known that an optical fiber with small dispersion in a transmission wavelength band, e.g., a dispersion shifted fiber (DSF) is disadvantageous in this respect.
Further, signal distortion due to self phase modulation (SPM) and cross phase modulation (XPM) is a very serious problem. A solution of such problems is researched and reported in OFC ""97 TuNlb, etc. These reports show that the enlargement of an effective core area (Aeff) as well as reducing a non-linear refractive index difference (n2) is very useful.
The present invention provides an optical fiber for restraining the non-linear phenomenon and an optical transmission line using this optical fiber. The invention resides in an optical fiber comprising:
a negative dispersion value in a range of xe2x88x9218 ps/nm/km or more and xe2x88x928 ps/nm/km or less in at least one portion within a wavelength range from 1500 nm to 1650 nm, and a negative dispersion slope;
a refractive index profile structure of n-layers (n is an integer of 4 or more) sequentially arranged in an order of a first layer, a second layer, a third layer, - - - from an inner side;
a relative refractive index difference (xcex941) of the first layer set to 0.75% or more and 0.90% or less in a state in which cladding layer of the refractive index profile is set to a reference; and
an effective core section area set to 32 xcexcm2 or more at a wavelength of 1550 nm.